1. Field of the Invention
The present invention concerns an edged ceramic member, and a manufacturing method thereof, a punch used for lead frames and a method of manufacturing lead frames.
2 Discussion of the Prior Art
Since zirconia series ceramics can develop toughness not found in usual ceramics, as a result of a stress relaxation mechanism based on stress-induced transformation of a partially stabilized zirconia phase, their application has made progress, for example, in molds or tools used for shearing such as punching or cutting or deep drawing, as well as in cutlery such as scissors or cooking knives.
Further, since such zirconia series ceramics can be improved in various characteristics inherent to zirconia and can be provided with new characteristics by compositing an appropriate second phase to the partially stabilized zirconia phase, more extended application uses are possible. For example, Japanese Patent Laid-Open No. 275977/1992 discloses a technique capable of increasing the flexural strength by a factor of two or more by incorporation of 20% by weight of alumina to zirconia. Further, Japanese Patent Laid-Open 221358/1997 discloses a technique for enabling electric spark discharge machining by incorporating electroconductive particles.
However, although improvement for various characteristics and provision of new characteristics are possible for the zirconia ceramic type ceramic members as described above at the laboratory level, troubles are often caused in the stage of developing them into actual products. Particularly, in those parts concerning molds requiring sharp edges (punches or dies), even ceramics of excellent flexural strength or hardness can not be used as parts for molds if edge portions are chipped, because they cause errors in the dimensional accuracy of products or form burrs, warps or flaws (marks) to works.
For example, lead frames used for the mounting of substrates of integrated circuit chips such as IC or LSI generally have shapes in which a plurality of leads corresponding to chip terminals of integrated circuits are arranged in complicated manners. While such lead frames were manufactured by chemical etching of metal plate blanks, an efficient manufacturing method by using punching has been adopted mainly in recent years along with a remarkable progress in mechanical working techniques. However, as can be seen from the fact that the etching was used, punching patterns for lead frames are extremely fine and even slight dimensional error or occurrence of burrs or warps results in a problem that directly leads to defects fatal to electric circuit parts such as contact failure with integrated circuit chips to be mounted and short-circuits. Accordingly, upon punching lead frames, higher dimensional accuracy is required for punched openings or finishing accuracy than that for other punched parts. Then, particularly accurate and sharp edge finishing are demanded for mold parts used for punching of such lead frames, particularly, for the edge of a top end surface of a punch that shears a metal blank plate between the edge and the inner edge of a die hole in a punching die, since even slight chipping or disturbance gives a direct effect on the accuracy of forming the punched openings.
In the case of a ceramic member requiring a sharp edge such as the punch or the die for use in the mold as described above, it is necessary to finally apply edge finishing by accurate grinding. However, in a case of existing zirconia series ceramics, there is a problem that such edge grinding tends to cause chipping at the edge portion. Therefore, a method of sacrificing the sharpness at the edge portion to some extent has been adopted for avoiding the occurrence of large chipping but this can not attain favorable working accuracy. However, if sharp edge finishing is performed excessively, chipping becomes significant making it sometimes impossible for the manufacture of products.
An object of the present invention is to provide an edged ceramic member and a manufacturing method thereof capable of effectively suppressing. the occurrence of chipping and, as a result, finishing the edge portion to such a sharpness as can not be attained so far and, thus, capable of remarkably improving the accuracy of working such as punching by using the same, as well as a punch for manufacturing lead frames capable of punching the lead frames at an extremely high accuracy and a method of manufacturing lead frames by using the ceramic member described above.
For achieving the foregoing object, the edged ceramic member according to the present invention is characterized by comprising a zirconia-containing ceramic material containing 20% by volume or more of a zirconia series ceramic phase mainly composed of a zirconium oxide, in which
the zirconia-containing ceramic material satisfies:
KC/(dA)xe2x89xa75xe2x80x83xe2x80x83(1)
by using an exponential value A set within a range from xe2x88x920.41 to xe2x88x920.37, d being an average grain size (unit: xcexcm) and KC being a fracture toughness value (unit: MPaxc2x7mxc2xd) thereof, and
one or more of edged portions each present in the form of a ridge at an intersection between two edge forming surface are formed to the outer surface of the member, and at least one of the edge portions is formed as a sharp edge portion having a width for the edge top end of 0.15 mm or less present on a cross section taken along an arbitrary plane in perpendicular to the direction of the ridge.
In the present invention, the average grain size d of the zirconia-containing ceramic material means a value obtained by mirror-finishing the surface of a material by surface grinding and lapping, thermally etching the same in a nitrogen atmosphere under a normal pressure at 1300xc2x0 C. conducing SEM observation (magnification: 5000xc3x97), and determining on an observed image as explained below. That is, crystal grains appearing on an observed image are approximated as a circles and the diameter distribution of them is determined and, further, a crystal grain size distribution is determined while approximating them as spheres by applying the Schwarts-Saltykov method (assuming the range for the grain size group as 0.1 xcexcm), and the central value for the grain size group at which the cumulative frequency from the side of the smaller grain size reaches 50% is defined as the average grain size d. Further, the fracture toughness value means a value measured by the SEPB method in accordance with JIS:R1607.
Since chipping tends to be formed in the zirconia-containing ceramics as described above, it has been considered impossible to form a sharp edge portion with a top end width for the edge of 0.15 mm or less by usual grinding. However, as a result of an earnest study by the present inventor, it has been unexpectedly found that occurrence of chipping can be prevented extremely effectively even when the sharp edge as described above is formed and the present invention has been accomplished. That is, in the edged ceramic member of the invention, an edged ceramic member with excellent chipping resistance can be obtained when the zirconia series ceramic phase of the composition described above is contained and when the value B defined by:
KC/(dA)= Bxe2x80x83xe2x80x83(2)
is 5 or more with the exponential value A being defined within a range from xe2x88x920.41 to xe2x88x920.37.
As a result, the accuracy for punching or the like by using the member can be improved remarkably.
When the exponential value A is out of the range from xe2x88x920.41 to xe2x88x920.37, the value B according to the formula (2) no more indicates the difficulty or easiness for the occurrence of chipping of the zirconia-containing ceramic material and it loses a meaning as an index representing the chipping resistance. Further, it is essential that the value B is 5 or more, and a greater value is more advantageous in view of ensuring the chipping resistance. However, since it is difficult to set the crystal grain size in the zirconia series ceramic phase to 0.1 xcexcm or less owing to the requirement in view of the manufacturing method (particularly, preparation of starting powder) and, correspondingly, the value B is often up to about 5. However, this does not define the upper limit in the invention. For improving the chipping resistance, it is desirable that the value B is 6 or more, preferably, 6.5 or more. As a result, as the value B increases, it is possible to finish the edge portion more sharply and, for example, it is preferred that the top end width for the edge is, for example, less than 0.1 mm and, more preferably, less than 0.07 mm as a more desired value.
In the sharp edge portion, since chipping giving an effect, for example, on the accuracy of punching or the like is no longer formed as a result, it is possible to make the maximum height Rmax to 70 xcexcm or less for the surface roughness at the edge chip measured in the direction of the ridge. The maximum height Rmax means that chipping is suppressed more as it is smaller. In this case, Rmax can be decreased further as the value B is larger and, for example, it is possible to provide the value Rmax of preferably 50 xcexcm or less, more preferably, 30 xcexcm or less.
It is known that ZrO2 and HfO2 as the main component of the zirconia series ceramic phase cause transformation between each of three kinds of phases of different crystal structures depending on the change of temperature and, specifically, they form a monoclinic system phase in a lower temperature region including room temperature, a tetragonal system phase in a higher temperature region and a cubic system phase in a further higher temperature region. When the entire zirconia series ceramic phase comprises at least one of ZrO2 and HfO2, it is considered that almost of them form the monoclinic system phase. However, it is known that transformation temperature between the monoclinic system phase and the tetragonal system phase is lowered and the tetragonal system phase can be stabilized in a temperature region near the room temperature by including in solid-solution an alkaline earth metal oxide or a rare earth metals oxide (for example, calcia (CaO) or ittria (Y2O3)) by a predetermined amount or more as a stabilizing ingredient in ZrO2 and HfO2,
In this case, it is known that the phase transformation from the tetragonal system phase to the monoclinic phase system is based on a so-called martensitic transformation mechanism or a similar phase transformation mechanism and, when external stress is applied, the transformation temperature rises and the tetragonal system phase causes a stress-induced transformation and the distortion energy given by the stress is consumed as the driving force for the transformation, so that the exerted stress is moderated. Accordingly, in a ceramic structure in which zirconia series ceramic phase particles containing such a tetragonal system phase are dispersed for instance, when chipping tends to occur during mechanical grinding for forming the sharp edge portion and if the zirconia type ceramic phase particles are present near the top end of a crack, the tetragonal system phase is transformed into the monoclinic system phase by the stress concentrated to the top end of the crack. This relaxes the stress localized to the top end of the crack to hinder or moderate the propagation of the crack.
It is considered that the fracture energy exerts exclusively in a direction of enlarging the crack by the elastic energy in other ceramic materials showing no stress relaxation by transformation, whereas it is considered for the zirconia-containing ceramic that volumic expansion in the transformation region formed to the top end of the crack exerts a compressive stress to a wake region adjacent the opening of the crack, which acts in the direction of closing the crack to suppress the preparation of the crack. Thus, distortion energy accumulation mechanism along with propagation of crack is greatly different between the zirconia-containing ceramics and other ceramics. It should be noted that the relation (1) described previously is effective only for the zirconia-containing ceramic material containing 20% by weight or more of the zirconia series ceramic phase and it can not be applied to other ceramics, for example, silicon nitride type ceramics in which the structure is formed of acicular crystal grains, ceramics with addition of SiC whiskers, glass ceramics in which a great amount of a glass ingredient phase is formed between individual crystal grains and polar ceramics such as refractories. While the reason can not be explained clearly, it may be estimated that the difference of the accumulation mechanism of the distortion energy described above between the zirconia series material and other ceramic material is concerned.
If the content of the zirconia series ceramic phase is less than 20% by volume, sufficient chipping resistance cannot be ensured. The content for the content of the zirconia series ceramic phase is desirably from 60 to 98.5% by volume. If the content of the zirconia series ceramic phase exceeds 98.5% by weight, sufficient density for a sintering product can not sometimes be obtained because of insufficiency of a sintering aid ingredient.
Further, the relative density of the zirconia-containing ceramic material is preferably 98% or more. If the relative density is less than 98%, sufficient flexural strength cannot be obtained, making it sometimes impossible to be used, even if the value B is 5 or more, depending on the purpose of use of the edged ceramic member (for example, a punch or a die for use in mold undergoing a strong impact and requiring an extremely sharp edge portion such as in lead frame punching to be described later). Further, if the content of the zirconia series ceramic phase is less than 20% by volume, the relative density can not sometimes be increased to 90% or more even if a pressure sintering method such as a hot pressing or HIP is adopted, and it can be said desirable to adjust the content of the zirconia series ceramic phase within the range described above also in view of securing the relative density.
In the edged ceramic member according to the invention, the zirconia series ceramic phase is mainly composed of the zirconium oxide but this is not restrictive and xe2x80x9cmain ingredientxe2x80x9d or xe2x80x9cmainly composed ofxe2x80x9d means 50% by weight or more in the present specification.
Further, as the stabilizing ingredient for the zirconia series ceramic phase, it is desirable to contain one or more of Ca, Y, Ce and Mg within a range from 1.4 to 4 mol % in total as the content in the zirconia series ceramic phase being expressed as the value for an oxide, that is, CaO for Ca, Y2O3 for Y, CeO2 for Ce and MgO for Mg, respectively. If the content of the stabilizing ingredient is less than 1.4 mol %, since the content ratio of the monoclinic system phase increases, the content ratio of the tetragonal system phase is lowered relatively failing to obtain a sufficient stress relaxation effect described above, so that the chipping resistance upon forming the sharp edge portion with the conditions described above may sometimes be insufficient. On the other hand, if the content of the stabilizing ingredient exceeds 4 mol %, the content ratio of the cubic system phase is increased and the chipping resistance may also be sometimes insufficient. The content of the stabilizing ingredient is preferably from 1.5 to 4 mol % and, more preferably, from 2 to 4 mol %.
As the stabilizing ingredient for the tetragonal system phase, specifically, Y2O3 is used suitably in the invention since the strength of the resultant ceramic material is higher and the cost is relatively inexpensive compared with the case of using other stabilizing ingredients. On the other hand, CaO and MgO can also be used suitably in the invention since the strength of the obtained ceramic material is relatively higher although not so remarkable as in the case of using Y2O3 and they are less expensive further compared with Y2O3. Y2O3, CaO and MgO can be used each alone or used in combination of two or more of them.
Then, since ZrO2 and HfO2 as the main ingredient of the ceramic particle body are similar in chemical and physical properties, they may be used either alone or used in combination of them. However, since ZrO2 is less expensive compared with HfO2, it can be said that the ceramic particle product is desirably constituted with ZrO2 as the main ingredient. While usually available ZrO2 raw materials at an ordinary purity often contain a trace amount of HfO2, there is scarce requirement of positively removing HfO2 contained therein with the reasons described above in a case of using such starting materials.
Further, in the zirconia series ceramic phase, it is desirable that the ratio CW/TW between the existent weight CW for the cubic system phase and the existent weight TW for the tetragonal system phase is less than 1. The tetragonal system phase is tended to be formed when the content of the stabilizing ingredient is increased to lower the transformation point relative to the tetragonal system phase or when the sintering temperature exceeds 1600xc2x0 C. and it has a property of tending to make crystal grains coarser during sintering compared with the monoclinic system phase or the tetragonal system phase. Then, grown crystal grains of the cubic system phase are easily detached since the boundary bonding force with respect to other crystal grains is small and, if the amount of the cubic system phase increases till the ratio exceeds 1, the amount of the grown crystal grains formed is also increased. They lead to degradation of the chipping resistance upon forming the sharp edge portion with the conditions described above. Therefore, the ratio CW/TW is preferably less than 1 and, desirably, less than 0.5 and, more desirably, less than 0.1.
Information regarding the existent ratio for the tetragonal system phase and the cubic system phase is obtained as below. For example, a portion of the ceramic material is mirror finished and X-ray diffractometry is conducted on the polished surface by a diffractometer method. In this case, in the obtained diffraction pattern, since (111) strength peak positions as the main diffraction peaks for the tetragonal system phase and the cubic system phase appear adjacent with each other, the existent amount for the monoclinic system phase is at first determined based on the ratio of the total intensity Im for (111) and (11-1) of the monoclinic system phase and the sum of It+Ic for the (111) intensity of the tetragonal system phase and the cubic system phase. Then, the sintered product is mechanically pulverized and X-ray diffractometry is conducted again to determine the (111) intensity Ixe2x80x2m and Ixe2x80x2c of the monoclinic system phase and the tetragonal system phase. In this case, since it is considered that the tetragonal system phase in the sintering product transforms into the monoclinic system phase by the mechanical stress accompanied by the pulverization, the existent amount for the cubic system phase can be determined based on Ixe2x80x2c/(Ixe2x80x2m+Ixe2x80x2c). It is desirable that the thus obtained value Ixe2x80x2c/(Ixe2x80x2m+Ixe2x80x2c) is 0.5 or less, preferably, 0.1 or less for improving the chipping resistance upon forming the sharp edge portion with the conditions as described above.
Then, the zirconia-containing ceramic material may be a composite ceramic material in which the matrix ceramic phase constituting a remaining portion of the zirconia series ceramic phase mainly comprises an electroconductive inorganic compound having at least one of Ti, Zr, Nb, Ta and W as the metal cationic ingredient and/or alumina. For example, when alumina is contained in the matrix ceramic phase, the flexural strength of the zirconia-containing ceramic material can be improved outstandingly, and the durability of the edged ceramic member when used for punching mold can be improved remarkably. In this case, it is preferred that the content of the zirconia series ceramic phase is from 20 to 80% by volume and the content of the alumina type phase mainly comprising alumina as the main ingredient is from 20 to 80% by volume in order to improve the chipping resistance upon forming the sharp edge portion.
On the other hand, the zirconia-containing ceramic material can be provided with electroconductivity and thus the ceramic material can. be applied with spark discharge machining such as wire cutting, by incorporating the electroconductive inorganic compound into the matrix ceramic phase. The electroconductive inorganic compound may be at least one of metal nitrides, metal carbides, metal borides, metal carbonitrides and tungsten carbide having at least one of Ti, Zr, Nb and Ta as the metal cationic ingredient and, specifically, it can include, for example, titanium nitride, titanium carbide, titanium boride, tungsten carbide, zirconium nitride, titanium carbonitride and niobium carbide. In this case, for improving also the chipping resistance upon forming the sharp edge while ensuring the electroconductivity for enabling spark discharge machining, it is preferred that the content of the zirconia series ceramic phase is from 20 to 80% by volume and the content of the electroconductive inorganic compound phase is from 20 to 80% by volume.
By the way, the edged ceramic member as described above can be used as a ceramic working tool for shearing, cutting and bending or deep draw using the sharp edge portion as a site of applying the working force. Since the edged ceramic member of the invention is formed with a sharp edge portion with less chipping-induced defects, working at high accuracy is possible by utilizing the same as a site of applying the working force.
Such a ceramic working tool is particularly effective when used as a punching tool for a lead frame required for punching a fine pattern at a high accuracy. Specifically, a lead frame can be manufactured by using the edged ceramic member of the invention as described below. That is, a metal plate blank is placed between the punch constituted as the edged ceramic member described above and a punching die having a die hole, and advancing the punch in this state relatively into the die hole along an axial direction thereby shearing the metal plate blank between the edge portion of the punch and the inner circumferential edge portion of the die hole. In this case, punched opening corresponding to the shape at the top end surface of the punch is formed to the metal plate blank.
Further, when the edged ceramic member described above is applied to a punch for manufacturing a lead frame, the following constitution can be exemplified as a preferred embodiment for preventing occurrence of chipping upon forming a sharp edge portion. That is, the punch for manufacturing the lead frame is formed with an edge portion at an intersection between the top end surface of the punch and the outer circumferential surface of the punch, the top end portion of the punch at least including the edge portion thereof comprises a zirconia-containing ceramic material having a relative density of 98% or more and satisfying:
KC/(dA)xe2x89xa75
by using an exponential value A set within a range from xe2x88x920.41 to xe2x88x920.37, d being an average grain size (unit: xcexcm) and KC being a fracture toughness value (unit: MPaxc2x7mxc2xd), and the volumic content of the zirconia series ceramic phase containing 50% by weight or more of a zirconium oxide is 60 to 98.5% by volume, and
the edge portion is formed as a sharp edge portion having a top end width for the edge of 0.15 mm or less present on a cross section taken along an arbitrary plane in perpendicular to the direction of the ridge, and a maximum height Rmax for the surface roughness on the top end of the edge of 50 xcexcm or less as measured in the direction of the ridge.
Then, the first method of manufacturing an edged ceramic member according to the invention is characterized by applying grinding to the outer surface of a zirconia-containing ceramic material containing 20% by volume or more of a zirconia series ceramic phase mainly composed of a zirconium oxide and satisfying:
KC/(dA)xe2x89xa75
by using an exponential value A set within a range from xe2x88x920.41 to xe2x88x920.37, d being an average grain size (unit: xcexcm) and KC being a fracture toughness value (unit: MPaxc2x7mxc2xd),
thereby forming a sharp edge portion present in the form of a ridge at an intersection between two edge forming surface having a top end width for the edge of 0.15 mm or less present on a cross section taken along an arbitrary plane perpendicular to the direction of the ridge and a maximum height Rmax of 50 xcexcm or less as the surface roughness on the top end surface of the edge as measured in the direction of the ridge.
When the values for KC and d of the zirconia-containing ceramic material are adjusted so as to provide: Bxe2x89xa1KC/(dA)xe2x89xa75, even when a sharp edge portion with the top end width for the edge of 0.15 mm or less is formed by grinding, the maximum height Rmax for the surface roughness on the top end surface of the edge can be reduced to 50 xcexcm or less. That is, a sharp edge portion with less chipping can be formed.
A second method of manufacturing an edged ceramic member according to the invention comprises a method of manufacturing an edged ceramic member by applying grinding to the outer surface of a zirconia-containing ceramic material containing 20% by volume or more of a zirconia series ceramic phase mainly composed of a zirconium oxide thereby forming one or more of edge portions present in the form of a ridge at an intersection between two edge forming surfaces characterized by, measuring an average grin size d (unit: xcexcm) and a fracture toughness value KC (unit: MPaxc2x7mxc2xd) of the zirconia-containing ceramic material before grinding, and then applying grinding only to the zirconia-containing ceramic material having d and KC satisfying:
KC/(dA)xe2x89xa75
by using an exponential value A set within a range from xe2x88x920.41 to xe2x88x920.37.
By measuring KC and d for the zirconia-containing ceramic material and examining whether Bxe2x89xa1KC/(dA)xe2x89xa75 is satisfied or not based on the measuring values before grinding, it can be judged that whether the material tends to cause pitching or not before conducting grinding. As a result, since it can be determined whether the material is suitable to the formation of the sharp edge portion or not even without conducting actual grinding, wasteful loss of applying working to a not suitable material can be saved, for example, in a mass production, and it greatly contributes to the shortening of the period of time for the development of a material or reducing the development cost for a material in the course of the developing stage.
Further, the zirconia-containing ceramic material can be produced, for example, as described below. At first, a starting zirconia material, a starting material containing second phase particles to form a matrix ceramic phase and a solvent (water or an organic solvent less reactive with the starting material such as ethanol) are at first mixed to prepare a slurry. There is no particular restriction on the mixing method and, for example, ball mill mixing, trommel mixing or attrition mill mixing can be adopted. Further, various kinds of additives, for example, a dispersant or a decoagulation agent such as ammonium polycarboxylate, a viscous binder such as polyvinyl alcohol or polyacrylate ester type emulsion or a plasticizer such as stearic acid, microwax or paraffin may optionally be added in this case. Further, an antistatic agent, a defoamer and the like can also be added simultaneously.
The thus obtained slurry is dried and pelleted by an appropriate method into a dry powdery pellet. As the dry pelleting method, a spray drying method, a freeze drying method a vacuum drying method and the like can be adopted. Among them, when at least one of metal nitrides, metal carbides, metal boride, metal carbonitrides and tungsten carbide comprising one or more of Ti, Zr, Nb and Ta as the metal cationic ingredient are used as the second phase grains in the spray drying method, the inlet temperature for a hot blow used for the spray drying is preferably set to 200xc2x0 C. or lower, more preferably, to 170xc2x0 C. or lower for preventing or suppressing oxidation of the starting material.
The dry powdery pellet obtained in this manner is molded into a desired shape of a ceramic member. As the molding method, mold pressing, cold isostatic pressing, slurry casting mold (slip casting), extrusion molding and injection molding can be adopted. Further, it is also possible to combine several of the methods described above such as applying a mold pressing at a low pressure followed by cold isostatic pressing.
The thus obtained molding product is sintered by an appropriate method into a sintering product. As a sintering method, an atmospheric pressure sintering method, a hot pressing method or a hot isostatic pressing (HIP) method can be adopted. Further, it is also possible to combine several of the methods described above such as sintering by the atmospheric pressure sintering followed by applying the hot isostatic pressing. As the sintering atmosphere, an oxidative atmosphere such as a surrounding air atmosphere is preferably used in a case of not containing the second phase particles or in a case of using alumina as the second phase particles, and an inert atmosphere (including vacuum atmosphere) or a reducing atmosphere such as a hydrogen atmosphere is desirably used in a case of using at least one of metal nitrides, metal carbides, metal borides, metal carbonitrides and tungsten carbide having one or more of Ti, Zr, Nb and Ta as the metal cationic ingredient. The sintering temperature can be set within a range from 1300 to 1900xc2x0 C., preferably, from 1400 to 1600xc2x0 C. Further, when the molding product contains organic additives (for example, dispersant, decoagulating agent, viscous binder, lubricant, antistatic agent or defoamer), it is preferred to apply calcination at 400 to 600xc2x0 C. prior to the sintering within the temperature range described above, so that the organic additive ingredients are previously decomposed, removed or reduced by evaporation.
To the outer surface of the thus obtained ceramic sintered body, grinding is applied for forming a sharp edge portion. In this case, the sharp edge portion having the top end width for the edge described above is finished by grinding, for example, for both of the two edge forming surfaces with a grinding stone. For example, in a case of using a rotational grinding wheel, a diamond grinding wheel of #200 to 800 according to JIS B 4130 is preferably used, and the direction of the rotation is preferably aligned with the direction of the ridge of the edge portion to be formed and the feeding direction of a work (sintered ceramic body) for further suppressing the occurrence of chipping. Further, it is preferred that the cutting amount per 1 pass is from 0.5 to 5 xcexcm and a work feed rate is 1 to 20 m/min based on the rotational circumferential speed of 1000 to 6000 m/min.